A new set of conjugated oligomers C6H5C = C -(1,2-discussed in light of electronic conjugation of the extended i~ C6H4C = C), -C6H, (10; n = 3 -7) comprised of acetylene and system. Thermolysis of oligomers 10 indicates that rearrangephenyl units linked together at the 1,2 positions of the aroment of the triple bonds occurs to form higher conjugated matic ring is introduced. The facile synthesis of these com-oligo(acenes). The topology of two members (10; n = 2, 3) is pounds is achieved through the Pd-mediated coupling reac-confirmed by X-ray analysis and reveals a propensity for intion of diiodo-and dibromobenzene with the appropriate ethy-tramolecular n-stacking of the phenyl rings leading to a helical nyl component. Spectroscopic data of the new compounds are arrangement. Scheme 1. Some known (1 -4) and new (5-9) phenyl-capped poly[l,2-phenylene(2,1-ethynediyl)] compounds 1 2 3 \ \ 4 \ YA, \ / 4 \ / 5 6 7 6

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The continuous supplementation of mice with supraphysiological doses of estrogen for the growth of estrogen receptor-positive breast cancers has been linked to toxicity in the host and perturbation of cancer cells' function that can misguide preclinical studies. Thus, alternative experimental models with circulating levels of estrogens higher than those of mice may represent more suitable hosts to model estrogen receptor-positive breast cancers. 23:11 Commentary I Chatzistamou and H Kiaris Breast cancer models Modeling estrogen receptor-positive breast cancers in mice: is it the best we can do?

Silver(1) and Copper(1) Complexes of 1,6-Cyclodecadiyne anThe reactions of 1,6-cyclodecadiyne (l), 1,?-cyclododecadiyne (2), and 1,8-~yclotetradecadiyne (3) with silver(1) triflate and copper (1) double-strands of 1,6-cyclodecadiyne rings in the chair conformation are coupled by Ag(CF3SO&Ag units to form a twodimensional network. The X-ray analysis of single crystals ofid 1,?-Cyclododecadiyne 6 and 7 reveals twelve-membered rings that are connected by silver or copper ions, respectively. Each triflate ligand in 6 and 7 uses two of its oxygen atoms to coordinate two different metal centers. The result is a complex three-dimensional network. In the case of the silver complex 8, the X-ray analysis also exhibits a similar polymeric structure. Only slight differences of the structural parameters are observed on comparison of the free cyclic dialkyne and that bound to a metal in 4, 6, and 7. The conformation of the 10-or 12 membered rings in 1 and 2 are more or less identical to those in 4 or 6 and 7.

If Angewandte Chemie had published "Highlights" twenty years ago, the topic of this article would certainly have been addressed then. The most recent reports from the research groups led by Nicolaou,"] Diederich, I2] V~l l h a r d t , [~~ and MyersC4] prove that the chemistry of conjugated enediynes continues to flourish. What is more remarkable, however, is the difference in the goals of the investigations of enediynes then and now. Twenty years ago the syntheses of new 4n and (4n + 2) n-electron systems and tetrahedranes were the main points under consideration; today's motivation for examining these compounds comes from natural products chemistry and from interest in new modifications of carbon.Biologically Active Anticancer Antibiotics: Nicolaou et al. were not only the first to complete the synthesis of the anticancer antibiotic cdkheamycin indeed a preparative masterpiece, they also contributed to the understanding of the mode of action of the aglycon (1) responsible for the DNA cleavage.[' b, The incorporation of the enediyne unit in the ten-membered ring of the aglycon enhances the reactivity of the already labile planar 6n-electron system; after activation by attack of a nucleophile, the triple bonds are even closer together and ring closure to give a 1,4-diradical (Bergman c y~l i z a t i o n ) [~~ is induced. For the systematic study of the mechanism of DNA cleavage cyclodeca-3-ene-l,5-diyne (2) was prepared as the most strained member of a series of monocyclic conjugated enediynes; because of the short transannular distance between the triple bonds (d = 3.25 in l), its cyclization via the 1,4-diradical3 to give tetralin (4) proceeds even at 50 "C. By determining the strucwhich d < 3.2-3.31 A, spontaneous Bergman cyclizations can be expected.Kinetics and Mechanism: First evidence that cyclization of conjugated enediynes proceeds via 1,4-didehydrobenzene intermediates like 6 was reported by Bergman et al. about twenty years ago[*' in an elegant study of the dideuterated parent compound, cis-hexa-3-ene-I ,5-diyne (5). Recently, the same research group examined an expanded system, (Z,Z)-deca-3,7-diene-I ,5,9-triyne (7), and proved that the analogous double cycloaromatization gives rise to 2,6-didehydronaphthalene (9),16] which is isolated as naphthalene (10) after H abstraction from the solvent. The cyclizations of both 5 and 7 are first-order reactions. The rearrangement of 5 to give deuterated benzene proceeds almost quantitatively at 190 "C in dilute solution and has an activation energy of 32 kcalmolIn contrast, the reaction of 7 (at 190°C) provides naphthalene in only 10% yield. tures of a number of model compounds Nicolaou et al. were able to predict whether an enediyne would undergo Bergman cyclization at room temperature, and thus be a potential anticancer drug. The transannular separation of the triple bonds serves as the decisive parameter; in compounds in [lO]annulene is outlined in Scheme 1. Key steps include the Pd-catalyzed Heck coupling of 11 and 12 to give 13, the chain extension by mea...